For the $ I say changing to radial tires via replacing your rear wheel and buying two new tires, and maybe replacing your steering head bearings, changing the fork oil, and using a pair of Progressive Suspension or Race-Tech springs w/either Gold Valve cartridge emulators or RICOR Intiminators to greatly-improve your handling would be where I would begin. That, and stainless steel brake lines, HH pads, and replacement of F & R brake fluid, and clutch fluid should get you enjoying your bike a whole-lot more.
Result:
- better handling from the front end
- better braking-your life is worth it, right?
- no more handling issues because of the radials and steering head bearings, and front fork overhaul
Cheap? Not really. Worth-it? If you rode your bike back-to-back w/it modded like this, you would know why the $ is very well-spent. Realistically, jet kits and exhausts, and airbox changes are what most people want to do first, but being able to have a better-handling bike and being able to use the performance it has, safely, will reward you far-more than the jet kit and loud exhaust.
Save your $ for the braking improvements (#1), the rear wheel & radials (#2), and the front end work (#3). That's how I would list them in order of results. Brakes first, because ya gotta live to do the other stuff, brakes will certainly help there. You already have 4-piston, dual-pair, opposed calipers.